1. Field of the Invention
The present invention relates to a storage, and in particular to a disk array apparatus which stores data in one or more disk devices, and a storage system including plural disk array apparatuses.
2. Description of the Related Art
Sizes of storages used in companies and the like are increasing year after year. In order to cope with this increase in sizes, a technique called a disk array, which connects plural storages and operates the storages as one storage system, has been devised.
FIG. 2 is a diagram showing an example of a structure of a conventional disk array apparatus (U.S. Pat. No. 6,477,619). As shown in FIG. 2, the disk array apparatus includes plural storages (here, disk devices) 202 and a disk control apparatus 210 that controls the plural storages 202. The disk control apparatus 210 includes: channel interface (hereinafter referred to as “channel IF”) units 204 for performing data transfer between a computer, which uses the disk array apparatus, and the disk control apparatus 210; disk interface (hereinafter referred to as “disk IF”) units 205 that execute data transfer between the disk devices 202 and the disk control apparatus 210; and memory units 208 that are cache memories storing data read and written between channel IFs and disk IFs or shared memories storing control information on a disk array (e.g., control information on data transfer between the channel IF units 204 and cache memories). Further, the channel IF units 204, the disk IF units 205, and the memory units 208 are connected to one another by a mutual connecting network 207.
A request of users with respect to scalability of performance of a disk array apparatus is strict. It is necessary to design the disk array apparatus such that one disk array apparatus can be extended to cover various disk array apparatuses ranging from a smaller disk array apparatus to a large disk array apparatus. In the case in which it is attempted to secure scalability in a disk array apparatus of a conventional technique, it is necessary to incorporate a mechanism for making it possible to add devices (e.g., interface for expansion: hereinafter referred to as “expansion feature”) in a disk control apparatus of the disk array apparatus in advance. However, on the other hand, a request for a reduction in cost for the disk array apparatus is also strict. If the expansion feature is simply installed in the disk array apparatus, cost for installing the disk array apparatus becomes comparatively high for a user (especially for a user who does not require scalability). In addition, since a minimum unit in the case of expansion is a channel IF or the like, there is little degree of freedom of scalability.
On the other hand, as a technique for securing scalability, there is also a technique called a storage area network (hereinafter referred to as “SAN”) in which individual disk array apparatuses are connected by a fiber channel or the like. However, in the case in which a large storage system is constituted by the SAN, cost for installing switch fabric, which realizes SAN connection, is required in addition to cost for the disk array apparatuses. In addition, in the case in which the disk array apparatuses are connected to one another by the SAN, since channel IF units, which should originally be connected to a computer, are used for the connection with the SAN, the number of interfaces, which can be used for data transfer between the computer and the storage system, is reduced.
Moreover, in order to secure performance desired by a user, an appropriate increase or reduction of apparatuses and evaluation thereof (if the performance can be secured) are required to be performed. However, this point is not taken into account in the conventional technique.